Overspeed control means for a gas turbine engine



Feb. 23, 1965 D. CARRIIERE ETAL 3,170,548

OVERSPEED CONTROL MEANS FOR A GAS TURBINE ENGINE Original Filed Oct. 30, 1961 2 Sheets-Sheet l 25-- 2500 M. dwnrMfl Y I l. INVENTOR.

1965 m. L. CARRIERE ETAL 39?,@.

OVERSPEED com'r sox, MEANS FOR A GAS TURBINE ENGINE Original Filed Oct. :50, -i951, 2 sheets sheet 2 jf w @w A 7'7'0 kmers United States Patent 3,170,548 OVERSPEED CONTROL MEANS FOR A GAS I TURBINE ENGINE Donald L. Carrier-e, Highland Park, James T. Laskey, Livonia, and Ivan M. Swatman, Birmingham, Mich, .assignors to Ford Motor Company, Dearborn, Mich,

a corporation of Delaware Original application Oct. 30, 1961, Ser. No. 148,603. Divided and this application Dec. 28, 1962, Ser. No.

248,010 3 Claims. (Cl. 192--3) This invention relates to a gas turbine engine and more particularly to a turbine overspeed speed control means.

This application is a division of our copending applica: tion S.N. 148,603, filed October 30, 1961.

ice

g which:

In gas turbine engines, the power turbine that is em- H ployed to drive a load usually operates at very high speeds.

wheel may burst due to the centrifugal force generated at these high speeds. 'Certain prior art systems attempt to control overspeed by means of a governor mechanism that acts to reduce the fuel supply to the engine. The time constant of these systems, however, is often so largethat the wheel bursts before the motive fluid supply to the engine can be substantially reduced.

The present invention provides a means for preventing the turbine wheel from reaching a speed that will cause the turbine wheel to burst due to'centrifugal force. This is accomplished by providing a brake mechanism that is designed to engage when the turbine reaches a'selected speed level over normal operating speeds. In the preferred embodiment of the invention, a stationary brake drum surrounds the turbine shaft and a pair of brake shoes are carried by the shaft. A bolt passing through the shaft holds the brake shoes in a position spaced from the brake drum during normal operating speeds of the turbine. This bolt has a section of reduced diameter that is designed to rupture due to the centrifugal force exerted upon it by the brake shoes when the speed of the turbine reaches theselected speed over normal operating speeds. The brake shoes then move into engagement with the brake drum and the speed of the turbine is stabilized and reduced.

The invention also provides a means for reducing or cutting off the fuel supply to the burner that provides motive fluid to the turbine. The movement of the brake shoes into engagement with the brake drum permits a control circuit that controls the fuel'supply to the burner to reduce or cut off the supply of fuel. In the preferred embodiment of the invention, this is accomplishedby providing a thermally responsive circuit breaker in the control circuit and by placing this circuit breaker in heat transferring relationship with respect to the brake drum. When the brake shoes engage the brake drum, the temperature of the brake drum will rise very rapidly thereby opening the circuit breaker, de-energizing the control circuit and cutting off the supply of fuel to the burner that provides motive fluid for the turbine.

An object of the invention is the provision of a turbine overspeed control means for a gas turbine engine.

Another object of the invention is the provision of a turbine overspeedcontrol means for a gas turbine engine that acts very rapidly to reduce the speed of a turbine that has reached overspeed conditions.

F161 is a sectional view, partially in elevation, through a portion of a gas turbine engine and a portion of the overspeed control mechanism of the invention;

along the lines 2-2 of FIG. 1, and 7 FIG. 3 is a schematic showing a means for controlling the fuel supply to a burner that supplies motive fluid to the turbine in response to overspeed conditions of the turbine. v

Referring now to the drawings in which like reference numerals designate like parts throughout the several views thereof, the numeral 10 designates a housing for a portion of the gas turbine engine of the present invention which carries the output shaft 12 of the engine. This housing is received in a casing 13 of the engine and is secured thereto by suitable means such as a plurality of bolts 14.

A turbine including wheel 15 and shaft 16 is rotatably mounted in housing 10by means of a pair of antifriction bearings 17 and 18. A sleeve 22 surrounds the shaft 16 and is keyed thereto by means of a key 23. This sleeve is forced against the inner race of bearing 18 by meansof a nut 24 threaded on the shaft 16. This in turn forces the inner race of bearing 17 against a shoulder on shaft 16. The wheel 15 and the shaft 16 are thus rotatably supported in the housing 10 and are positioned axially therein by the above described structure.

A turbine nozzle support'member 27 is positioned over the end of housing 10 and is aflixed thereto by a plurality of screws 32. A sleeve type bearing'33 positioned between the turbine nozzle support member 27 and the shaft 16 aids the bearings 17 and 18 in rotatably supporting the turbine wheel 15 and the shaft 16 within the housing.

A turbine nozzle, generally designated by the numeral 34, is supported from the nozzle support member 27 by a plurality of radial pins, one of which is shown at 41. A shroud 43 is supported from the tips of the blades of nozzle 34 and it extends radially and axially outwardly over the tips of turbine wheel blades 44.

A turbine scroll assembly is provided for supplying motive fiuidhot combustion gases from a combustion chamberto the turbine nozzle and the turbine. This scroll assembly comprises a scroll 46 having an inwardly extending flange 47 supported from the housing 10 by a pair of piston rings 48 and 49 and having an'outer flange 51 positioned by the casing member 13 throughfa plurality of bolts, one of which is shown at 52.

The above described structure is more fully disclosed in copending application S.N. 820,323, filed June 15, 1959, in the name of Ivan M. Swatman and assigned to the assignee of this invention.

FIGS. 1 and 2 show a mechanical means for stabilizing and reducing the speed of the turbine wheel 15 and shaft 16 when the turbine wheel exceeds a selected speed level over normal operating speeds. Such an overspeed condition may occur if the load is suddenly removed from the turbine wheel. In this invention a load is connected to the output shaft 12 which in turn is coupled toturbine wheel 15 and shaft 16 through an output gearing mechanism generally designated by the numeral 61. This gearing mechanism may include a spur gear 62 formed on the end of sleeve 22. The sudden removal of the load A further object of the invention is the provision of a A turbine overspeed control means for a gas turbine engine including a mechanical means that acts very rapidly to reduce the speed of a turbine that has reached overspeed condition and including an electrical means responsiveto may occur through a failure in the gearing 61 or in other coupling mechanisms that couple the output shaft 12 to an external load. If the wheel rotates at speeds greatly in excess of normal operating speeds it may be ruptured due to the high centrifugal forces developed and the particles thereof may be thrown through the casingof the engine.- This not only destroys the engine but it also. presents a hazard to personnel thatare located in the; vicinity of the engine- 1 I 'Themechanical' means mentioned above comp-rises a. centrifugal brake mechanism, generally designated by the numeral 63. T hs brake mechanism has a stationary mern,-

ber, preferably a brake drum 64 affixed to. the housing It? i by suitablefastening means, for example, machinev screws...

one of which is shownat 65. A pair of brake shoes 66' and 67are providedto cooperate with the brake drum;

'Each of these brake shoes has a face .ss defining one dicularly to the "axis of shaft 16 and by a second pair of spaced side walls extending in planes positioned .perpen dicula'rlydo the first mentioned set of parallel planes. The sleeve may also be provided with grooves 75 and '76 for receiving the main'body portion 69 of the brake shoes. Fastening means are provided for atlixingv the brake shoes to'the shaft 16 and for spacing the faces 6% from the brake drum 64 during normal operating condi.

tions of the, engine.) Thismea ns preferablytakes the cussed above provides a very excellent means for reducw ing or cutting off the fuel supply to the burner of the engine that supplies the turbine with motive fluid.

form of a boltfil having an enlarged head 82 engaging a the brake shoe 6'7 and a threaded end 33 engaging the brake shoe 6%. The central portion of the bolt "passes through a bore 8- inthe shaft 16,.and it includes a necked" down portion or portion'of reduced diameter 85.

In operation, the brake shoes and d7 rotate with the pointed out above, the bolts provides a means for positioning the faces 68 in spaced relationship from the brake 64. This situation prevails during all normal operating speeds of the engine. If for some reason, however, the engine should overspeed and reach a selected speed level above normal operating speeds, the brake shoes 66 and 67 will exert a large force on the bolt 81 due to the centrifugal force generated at these high speeds. This force will be sufficient to either rupture or elongate the neckeddown portion .85 of the bolt $1 sufficiently to permit the brake shoes66 and .67 tomove outwardly so that the faces 68 engage the brake drum 64. Itcan be appreciated that this will require. relative little movement and thatthc apertures 72 and 73 and the grooves 75 and 76 in the sleeve 22 provide a guidemeans for this movement.

These apertures and grooves in cooperation with the main body portion 69 and the reduced portion '71 of the brake shoes retain a driving relationship between the brake shoes and the turbine shaft 16.

7 in the-range of 37,500 rpm. at full speed and load. The

turbine wheel 15, the shaft 16 .and the sleeve 22-... As v high of 1000 F. a short timeafter engagement. necessary, therefore, to select a materialfor theseselements that will operate for at least a short period oftime at these temperatures. SAE 4340 steel-hardened to a Brinell hardness number of 352, which has a short time tensile strength of 103,500 p.s.i. at a temperatureof a thousand degrees Fahrenheit, is aisuitaole material, and eitherthe brake drum or the faces of the brake shoes should be chrome plated to reduce the possibility of galling. The bolt'al may be constructed of 'SAE'4140 steel hardened to a Brinell number ranging from 468 197;

The rapid 'risein temperature of the brake drum dis- Referringnow-to FIG. 3 there 'is shown a burner or combustion chamber 91 that is supplied with fuei througha fuel line 92. An electrically operated v valve, generally designated by the numeral 93, preferably a solenoid operated valve that is, normally closed when unenergized, is employed to control the supply of fluid to-the burner.

This valye includes arod 94 'constructedof magnetic material that-is biased to engage'valve seat 95 by means of aspring 96. This spring abuts theendof the rod 94 and a support member 97positionedwithin the. turbine. The

electrically operatedvalve 93also includes a winding ht} positioned around'the rod 94 and having one end grounded through a lead 101. The other end ofthe winding 93 is connected through a lead M2150 a .thermally respon'sive to the brake drum 64, forexample, the-fuse 103 may be mounted in direct contact with theibrake drum 64. This thermally responsive circuitbreaker should beidesigned necked down portion 85 of the bolt 31 may be designed to elongate or rupture when. the turbine speed reaches a speed of 42,000 r.p.m. Thisis considerably below the burst velocity of the turbine wheel which may be in the neighborhood of 70,000 r.p.m. When the faces 68 come into engagementwith the brake drum 6 the speed of the turbine will be stabilized at 42,000 r.p.m. for a short period of time and then will be substantially reduced even though full power is still being applied to the turbine by motive fluid flowing through the scroll 46 and the nozzle 34. It can be appreciated that very high temperatures will be developed'in the brake drum and the brake shoes as the result of the very rapid relative motion between these two members and because of the energy that needs to be dissipated. It is estimated that the temperatures may rise from a normal of between and 200 F. when the brake mechanism is not engaged to a to open when the temperature of the clutch drum has risen several hundred degrees over normal operating temperature as a result of the engagement of the brake shoes with the brakedrum. v

Thus, during normal operating conditions-of the engine the control circuit described above is energized as shown in FIG. 3 with'the winding-98 of the electrically operated valve energized'frorn battery 104 through switch "105 and fuse 103; Thisraises the rod 94 from the valve seat 95 and permits a full flow of fluid to the burner 91. The throttle controls for controlling the exact amount of the fuelto be fed to the burner 91 through the conduit 92 in response to ambient conditions andthe load on'the engine has. notbeen illustrated.- 'As shown, the electrically operated'valve 93 reduces or preferably completely shuts off the fuel to the burner in response to overspeed condi tions,

When overspeed'conditions are reached andthe faces 68 of brake shoes 66 and 67 come into contact with brake drum 64, the'very rapid .rise in temperature that results will open the control circuit for the valve 93 by melting thefuse 103 or by operating any other thermal responsive circuit breaker that may be-employed as an equivalent of the fuse. This immediately de-energizes the winding 98 and therod 94will come into contactwith. the valve seat 95 under the impetus of spring 96. This shuts olf the fuel to the burner M and hence reduces and in time cuts off the I motive fluid supplied to the turbine wheel 15, from the burner 91 through the scroll 46 and the turbine nozzle 34. Thus, the present invention provides a means for immediately reducing the speed of a turbine that has reached overspeed or runaway conditions." This is a mechanical means that will act almost immediately and very rapidly V to do this job. In addition, there-isprovided a means It is i limited to the exact constructionshown and described, but that various changes and modifications may be made Without departing fromthe spirit and scope of the invention, as defined in the appended claims.

We claim:

1. In a gas turbine engine, a housing, a turbine and a turbine shaft rotatably mounted within said housing, means mounted within said housing for supplying motive fluid to said turbine, a burner connected to said means, fuel supply means connected to said burner for supplying fuel thereto, a centrifugal brake mechanismcoupled between said housing and said shaft, said centrifugal brake mechanism including means for bringing said centrifugal brake mechanism into engagement when the speed of the shaft reaches a selected level, a fuel control means connected to said fuel supply, said fuel control means including means positioned in heat transferring relationship to said centrifugal brake mechanism and responsive to the heat generated by the engagement of said centrifugal brake mechanism for reducing the fuel supply to said burner.

2. In a gas turbine engine, a housing, a power turbine rotatably supported within said housing, a burner connected to supply motive fluid to said turbine, an electrically operated control means for controlling the supply of fuel to said burner, a source of electrical energy, a thermally operated circuit breaker adapted to open when its temperature exceeds a selected level, said electrically operated control means being energized to supply fuel to said burner from said source of electrical energy through said thermally operated circuit breaker, a centrifugal overspeed brake mechanism having movable means coupled to said shaft and stationary means supported by said housing, said movable means engaging said stationary means under overspeed conditions of said turbine and said shaft, said engagement resulting in a rapid rise in temperature of said stationary means to a value in excess of said selected level, said circuit breaker being positioned in heat transferring relationship with respect to said stationary means whereby said circuit breaker will open and said control means will be tie-energized to cut off the fuel supply to said burner.

3. In a gas turbine engine, a housing, a power turbine including a shaft rotatably supported within said housing, means for supplying motive fluid to said power turbine, said means including a burner, means including a fuel conduit connected to said burner for supplying said burner with fuel, a normally closed solenoid operated .valve positioned within said fuel conduit, a battery, a fuse, said battery being connected through said fuse to energize and open said solenoid operated valve, a centrifugally operated brake mechanism, said centrifugally operated brake mechanism including a brake drum aflixed to said housing and a pair of brake shoes coupled to said shaft and adapted to move into engagement with said brake drum due to centrifugal force developed when the speed of said turbine reaches a selected level above the normal operating speed range of the turbine, said fuse being positioned in heat transferring relationship with respect to said brake drum, whereby the heat generated by the engagement of said brake shoes with said brake drum melts said fuse thereby de-energizing and closing said solenoid operated valve.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A GAS TURBINE ENGINE, A HOUSING, A TURBINE AND A TURBINE SHAFT ROTATABLY MOUNTED WITHIN SAID HOUSING, MEANS MOUNTED WITHIN SAID HOUSING FOR SUPPLYING MOTIVE FLUID TO SAID TURBINE, A BURNER CONNECTED TO SAID MEANS, FUEL SUPPLY MEANS CONNECTED TO SAID BURNER FOR SUPPLYING FUEL THERETO, A CENTRIFUGAL BRAKE MECHANISM COUPLED BETWEEN SAID HOUSING AND SAID SHAFT, SAID CENTRIFUGAL BRAKE MECHANISM INCLUDING MEANS FOR BRINGING SAID CENTRIFUGAL BRAKE MECHANISM INTO ENGAGEMENT WHEN THE SPEED OF THE SHAFT REACHES A SELECTED LEVEL, A FUEL CONTROL MEANS CONNECTED TO SAID FUEL SUPPLY, SAID FUEL CONTROL MEANS INCLUDING MEANS POSITIONED IN HEAT TRANSFERRING RELATIONSHIP TO SAID CENTRIFUGAL BRAKE MECHANISM AND RESPONSIVE TO THE HEAT GENERATED BY THE ENGAGEMENT OF SAID CENTRIFUGAL BRAKE MECHANISM FOR REDUCING THE FUEL SUPPLY TO SAID BURNER. 